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Old 01-01-2016, 10:28   #1
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Yanmar Alternator Problem


I have a Yanmar 2gm20 with a Hitachi 55amp alternator. Charge from the alternator is split between 2 leisure batteries using a Multi battery isolator from sure power industries Inc.

I put a multimeter across the batteries with the engine running, and 15.2V appeared, with around 15.7 volts from the alternator (when I put the multimeter across alternator positive on the battery isolator and negative terminal on battery ). Even though 15.2V appears, the charge light on the engine panel is off for just a few seconds then illuminates. Also on my battery switch, when I select 1,2 or both batteries, both batteries receive 15v anyway! Which did not happen normally.

Any help would be greatly appreciated!
david1993hunter is offline   Reply With Quote
Old 01-01-2016, 10:44   #2

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Re: Yanmar Alternator Problem

Rashly assuming the voltmeter is accurate, the 1/2 volt difference from the battery to the alternator could just be the nornmal drop caused by a diode isolator. Which is 1950's technology and a waste of power at best today, better to get rid of it and use something like an Echocharger or West/Yandina Battery Combiner.

But the 15.7 on the alternator itself would indicate a defective internal regulator. Anything over 14.4 is a defective regulator, normally. And that excess voltage will damage your batteries, blow out your light bulbs, kill your onboard electronics....

All very good reasons to pull the alternator without using it at all any more, and get it shoreside for bench testing and an overhaul or replacement. And in the meantime, you can search on how and why to replace that battery isolator with some new 30-year technology instead.(G)
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Old 01-01-2016, 11:08   #3
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Re: Yanmar Alternator Problem

Thanks for your reply!

The regulator failed 2 or so months ago, and recently I found out that my boat wasn't earthed properly and the anode had no wear. Could that be related? Before when the anodes were ok and boat was earthed i didnt have any issue for a few years. Im not sure if that could have caused it!

I had considered a Sterling Alternator regulator so that will definitely be my next buy!
david1993hunter is offline   Reply With Quote

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